Vapor thermographic duplicating process

ABSTRACT

Heat activated duplicating process involving the steps of forming a coating on localized areas of a master sheet by transfer thereto from a transfer sheet, the coating being in the form of a discontinuous layer containing light colored normally stably solid, vaporizable first reactive material together with a particulate material and a minor amount of binder, placing the master sheet against a first receptor copy sheet which contains a second reactant material which coreacts with said first reactant to form a visible image, and subjecting the combined sheets to heat to vapor transfer a portion of the first reactant material, whereby an image is formed on the copy sheet, and repeating the heating step with additional receptor copy sheets to form additional copies.

Appl. No.: 161,850

Related US. Application Data Continuation of Ser. No. 781,195, Dec. 4, 1968, abandoned.

References Cited UNITED STATES PATENTS 7/1966 Gordon ..l0l/469 12/1969 Clark etal ..ll7/36.2

United States Patent 1 [111 3,722,406

Strong 1 Mar. 27, 1973 [54] VAPOR THERMOGRAPHIC 3,332,347 7/1967 Gundlach et a1. ..101/470 DUPLICATING PROCESS 3,459,581 8/ 1969 Newman 101/473 [75] Inventor: Doyle L. Strong, St. Paul, Minn. Primary Examiner David K1 ein [73] Assignee: Minnesota Mining and Manufactur- Attorney-Kinney, Alexander, Sell, Steldt & Delahunt ing Company, St. Paul, Minn. [22] Filed: July 12, 1971 [57] ABSTRACT Heat activated duplicating process involving the steps of forming a coating on localized areas of a master sheet by transfer thereto from a transfer sheet, the coating being in the form of a discontinuous layer containing light colored normally stably solid, vaporizable first reactive material together with a particulate material and a minor amount of binder, placing the master sheet against a first receptor copy sheet which contains a second reactant material which coreacts with said first reactant to form a visible image, and subjecting the combined sheets to heat to vapor transfer a portion of the first reactant material, whereby an image is formed on the copy sheet, and repeating the heating step with additional receptor copy sheets to form additional copies.

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1 VAPOR THERMOGRAPHIC DUPLICATING PRDCESS This is a continuation of application Ser. No. 781,195, filed Dec. 4, 1968 and now abandoned.

This invention relates to a novel dry duplicating process. More particularly, the invention relates to a thermographic duplicating process utilizing vaporizable colorless or light colored reactants carried in a coating on a master from which they are vapor transferred to successive copy sheets.

Spirit duplicating processes have long been used where it has been desired to form a large number of copies from a master. These processes, however, have several notable disadvantages in that the copy paper must be wetted with solvents which are volatile and combustible. This method also requires relatively complicated equipment for storing and dispensing the volatile liquids.

Various dry hectograph processes have been proposed. For example, in U. S. Pat. No. 3,252,413 (Sharkey), issued May 24, 1966,,it was proposed to physically transfer molten material from a master sheet to a succession of copy sheets. in this process, however, since a physical transfer of liquid materials is involved and since the sheets must come into firm contact in order for an image to be formed, i.e., any folds or irregularities in either of the sheets may cause ghosting or skipping of portions of the material to be copied. On the other hand, if the pressure on the sheets is too great, an undue amount of the liquid may be transferred to the first few copies whereby the number i of legible copies obtainable is greatly reduced.

Briefly summarized, the method of duplicating of this invention comprises the use of a transfer sheet formed from a base sheet having a continuous, i.e. coextensive transfer coating on its surface, the transfer coating being in the form of a discontinuous, ize. particulate layer containing a colorless or light colored, though normally stably solid, vaporizable first reactive material and a minor amount of a film-forming binder. Thecoating is transferred to a master sheet in localized areas which coincide with the imagesto be formed, for example, by overlaying the master sheet and the'transfer sheet and typing or writing on the master sheetQEach copy is made by placing the master sheet against a receptor copy sheet containing a second reactant material coreactive with the first reactant to form a visible image, and subjecting the juxtaposed sheets to heat, for example, by heated rollers or a heated shoe, to vapor transfer a portion of the first reactant material to each successive copy sheet whereby an image is formed on each copy sheet. The present invention provides a fast, clean, high quality duplicating system for making.

copies similar to those produced by spirit duplicating, but without the mess and cost of the solvent required in a spirit system. The system lends itself to use in a variety of means, including simple hand crank operated heating rollers, which are readilymade portable. If the master sheet bears infrared ray absorbing images, existing infrared type copiers such as those marketed under the trademark Thermo-Fax, can be used. Various machines having-automated feeding mechanisms can also be employed.

The invention will be further explained with reference to the accompanying drawings wherein:

FIG. 1 is a greatly magnified partial cross-sectional view illustrating the formation of a master sheet from a transfer sheet, and

FIG 2 is a cross-sectional view illustrating the formation of a copy.

Referring more particularly to FIG. 1, there is seen a transfer sheet 10 formed from a base sheet 12, usually paper, having a coating thereon 14, which contains a colorless reactant in a discontinuous matrix which also contains a minor amount of a film-forming material. Thus, layer 14 is formed from a mixture that is partially particulate and partially film-forming in order that, a stable coating may be formed on the base sheet 12 whichis sufficiently discontinuous to permit portions of the coating to be picked off in selected areas 16 onto a master sheet 18. Type keys or the like 20 can be used to press the master l8'against the transfer sheet 10 in the selected areas 16 to cause localized transfer of the coating 14.

FIG. 2 illustrates the formation of an image ona copy sheet 22. By means of heat, illustrated by arrows 26, a portion of the colorless reactant from image portions 16 is vapor transferred to coating 24 which contains a colorless coreactant. The two colorless coreactants then chemically react to form a colored image in areas 28 on the copy sheet 22.

As noted above, the transfer sheet is coated with a discontinuous coating which is partially particulate and partially film-forming. The particulate portion may be a paraffin wax, or other wax such as carnauba wax, bees wax, or a waxy compound such as cetyl alcohol. Other suitable waxes include polyethylene glycols sold under the trade name Carbowax. Alternatively, the particulate material can be an inorganic material such as finely divided silica. The film-forming constituent can be ethyl cellulose, polyvinyl acetate, or polyvinyl butyral, or various other film-forming polymers known to those skilled in the art.

In order to achieve the best transfer of the coating from the'transfer sheet to the master sheet, the paper for the master sheet should be somewhat open. This also allows for penetration of the coating into the sheet, thereby minimizing physical transfer in the copying step. Bond paper has been found well-suited for this purpose. If desired, the master sheet can be run through a heating means priorto formation of the first,

copy in order to drive the image forming coating into the paper of the master sheet thereby preventing excessive transfer of reactant to the first few copy sheets.

A variety of colorless or light colored reactants can be used in the practice of the invention. The reactant on the master sheet must be sufficiently volatile to be capable of vapor transfer from the master sheet to suecessive receptor sheets. The compound also must not be excessively volatile in order to prevent transfer of all of the compound during the formation of the first one or few copies. Normally the coreactant on the copy is in a coating thereon. This coreactant may, however, be distributed among the fibers of the copy sheet, for example, by adding it to the paper-making slurry during formation of the receptor paper.

In the following Table l are given examples of pairs of reactants which can be used inthe practiceof the invention. Any one of the reactants listed under a specific number in the column headed .Master Sheet can be used with any one of the corresponding coreactants under the same number in the column headed receptor protocatechuic acid isopropyl catechol thiourea gallic acid S-hydroxyquinoline l-hydroxy-4methoxynaphthalene (silver compounds only) 2. l-naphthaldehyde benzoylhydrazone (dimethylglyoxime 3. dithiooxamide N, N'-dibenzyldithiooxamide N, N'-dimethyldithiooxamide N, N'-2-hydroxyethyl dithiooxamide thiourea Receptor Sheet 1. ferric stearate ferric rosinate ferric laurate silver behenate silver stearate octadecylamine vanadate 2. (nickel stearate (nickel rosinate (nickel acetate 3. nickel stearate nickel rosinate copper rosinate copper acetate cobalt stearate cobalt naphthenate nickel oleate cadmium rosinate 4. cobalt acetate 5. methyl orange reaction product of malachite green-octadecyl amine 6. ammonium molybdate 7. zinc rosinate nickel rosinate nickel acetate zinc stearate 8. ferrous salts 4. ammonium thiocyanate 5. oxalic acid 6. S-hydroxyquinoline 7. diphenyl carbazone S diphenyl carbazide 8. a, a'-dipyridyl coreactive metal compound, especially nickel rosinate.

The invention will be further explained by means of the following illustrative examples wherein all parts are.

given by weight, unless otherwise indicated.

EXAMPLE 1 N,N'-dibenzyldithiooxamide parts Tributylphosphate 3 parts Dicyclohexylphthalate 2 parts (Carboxwax 6000) 19 parts Ethyl cellulose (Ethocel N-300) 1 part Acetone 65 parts The above mixture is placed in a ball mill and milled for 6 hours, or until a finely divided dispersion is obtained. This dispersion is coated to a 4.5 to 5.5 lbs/1,300 ft (16.9 to 20.6 gm/m) coating weight on a glassine-type paper (20 lb. per 3,000 ft ream or 32.06 gm/m). The coating may be applied by a number of techniques, but a reverse roll coater or knife coater works well.

This type of a formulation provides a coating that adheres well to the glassine base paper, but which is also partially discontinuous so that physical transfer from the intermediate transfer sheet to the master sheet is quite sharp and well-defined.

A range or papers is suitable for the master sheet, but a bond-type paper is preferred. This provides a good receptive surface for the wax transfer and facilitates the formation of sharp, clean-cut images.

To produce the copy, the imaged master sheet is placed in contact with a reactive receptor sheet and heat is applied (for example, in the 100 to 150 C. range) in the form of a hot roll, a hot shoe, a hot platen, or by the use of infrared radiation. The bond-type receptor sheet is coated with the following formulation at a coating weight of 1.5 lbs/1300 ft (5.6 gmlm Starch 24.1 parts Nickel nitrate 4.0 parts Sodium rosinate 15.7 parts Paper grade alumina 42.0 parts Calcium carbonate pigment 6.0 parts Thiourea 6.1 parts Sodiumsalt of condensed naphthalene sulfonic acid (Tamol SN) 2.0 parts The imaged receptor copy preferably comprises a light colored sheet with a strongly contrasting blue-purple image. One hundred or more copies can be made from a single master simply by repeating the last step with a new receptor sheet.

EXAMPLE 2 N,N'-Dibenzyldithiooxamide 10 parts Tributylphosphate 3 parts Dicyclohexylphthalate 2 parts Castor wax 10 parts Ceresin wax 1.8 parts Ethyl cellulose 0.2 part Acetone 72 parts Methanol 36 parts This formation is also ball-milled and then coated onto glassine paper at 4 to 5 lbs/1,300 ft (15 to 18.8 gm/m). In this case, castor wax (mp 186F. or 86 C.) is the main wax ingredient, and its higher melt temperature provides additional ambient storage stability.

EXAMPLE 3 The following formulation was coated on glassine paper at a coating weight of from 2 to 6lbs/l,300 ft (7.5 to 22.5 gm/m'). Generally the higher the coating weight, the larger the number of possible copies from a single master.

Dithiooxamide 4.8 parts Tributylphosphate 7.2 parts Polyethylene glycol (Carbowax 4000) 19.7 parts Acetone 59.5 parts Toluene 8.8 parts This intermediate wax transfer paper is used to make sharp copies with a contrasting blue image using receptor paper as described in Example 1.

EXAMPLE 4 Methyl gallate 46 pan; Mineral oil l5 parts Castor wax 29 parts Cerelin wax to m This intermediate transfer sheet was used to make a master that produces black-image copies on a receptor paper coated with silver behenate or ferric stearate in a binder, e.g., polyvinylacetate or ethyl cellulose.

EXAMPLE 5 Another color system which is applicable in the practice of this invention involves a leuco dye imaged onto an acidic receptor sheet, for example, paper coated with an acidic clay such as Attapulgite clay.

Substituted triphenyl methane color precursor (National Aniline No. l) parts Tributylphosphate 5 parts Carbowax 4000 (see Example 3) 19 parts Ethyl cellulose 1 part Acetone 65 parts The coating weights and procedures, formation of the master, and copying process, are similar to those described in Example 1.

EXAMPLE 6 Dithiooxamide 4 parts Castor wax 8 parts SAE motor oil 2 parts Toluene 12 parts Acetone 74 parts This was coated at 5 lbs/1,300 Ft (18.8 gm/m' on A mil 0.013 mm polyester film. Copies were formed on receptor sheets the same as described in Example 1.

The master sheet for duplicating is prepared by overlaying the transfer sheet and the master sheet together with the original to be copied and passing the aligned sheets past a source of intense infrared radiation, e.g., through a Thermo-Fax machine. The image areas of the original absorb the infrared radiation causing a temperature increase in the image area which allows transfer of the wax-like coating of the transfer sheet to the master sheet in the image area only.

The receptor copies are then prepared in the same manner as described in Example 1.

EXAMPLE 7 A transfer sheet is made by coating the following dispersion onto the glassine paper described in Example l at a coating weight of 5.5 lbs/1,300 ft (20.5 gmlm Cellulose acetate butyrate 10 pans N,N'-Dibenzyldithiooxamide 10 parts Tributylphosphatc 30 parts Finely divided silica (Syloid 10 parts Acetone 60 parts Copies were made as described in Example 1 on the copy paper described therein.

What is claimed is: 1. A method of du licating comprising: uxtaposing a mas er sheet and a transfer sheet said transfer sheet comprising 7.5 22.5 grams per square meter of surface of said transfer sheet of a layer comprising a light colored, normally stably solid, vaporizable first reactant material intimately admixed with a particulate material, applying pressure in localized areas of a first surface of said master sheet, said localized areas corresponding to an image to be duplicated, thereby transferring portions of said layer to localized areas of a second surface of said master sheet, said localized areas of said second surface correspondirig to a mirror image of said image to be duplicated, and thereby causing penetration of said portions of said layer into said master sheet,

juxtaposing said master sheet having said localized portions of said layer and a first copy sheet, said first copy sheet containing a second reactant material coreactive with said first reactant material to form a visible image,

subjecting the said juxtaposed. master and first copy sheet to at least C. of heat to vapor transfer portions of said first reactant material from said master sheet to said first copysheet whereby a said image to be duplicated is formed on said first copy sheet, and

repeating said juxtaposing and said heat transfer steps with additional copy sheets to form a said image to be duplicated on said additional copy sheets.

2. The process according to claim 1 wherein said first reactant material is selected from dithiooxamide and N,N'-di-substituted derivatives thereof and said second reactive material is selected from the stearates, rosinates, and oleates of nickel or copper.

3. The process according to claim 1 wherein said layer contains tributyl phosphate.

4. A process according to claim 1 wherein said particulate material ofsaid layer comprises a wax.

5. A process according to claim 1 wherein said transfer layer contains a minor amount of a film-forming binder.

6. A process according to claim 1 wherein said layer contains tributyl phosphate and. a wax, said first reactant material is selected from dithiooxamide and the N,N'-di-substituted derivatives thereof, said master sheet is an open bond sheet, and said transfer sheet is a glassine-type paper, and said layer of said transfer sheet comprises at least about 15 percent by weight of said first reactant material.

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2. The process according to claim 1 wherein said first reactant material is selected from dithiooxamide and N,N''-di-substituted derivatives thereof and said second reactive material is selected from the stearates, rosinates, and oleates of nickel or copper.
 3. The process according to claim 1 wherein said layer contains tributyl phosphate.
 4. A process according to claim 1 wherein said particulate material of said layer comprises a wax.
 5. A process according to claim 1 wherein said transfer layer contains a minor amount of a film-forming binder.
 6. A process according to claim 1 wherein said layer contains tributyl phosphate and a wax, said first reactant material is selected from dithiooxamide and the N,N''-di-substituted derivatives thereof, said master sheet is an open bond sheet, and said transfer sheet is a glassine-type paper, and said layer of said transfer sheet comprises at least about 15 percent by weight of said first reactant material. 